Dear filmmakers, especially independent filmmakers:
Story is the number one reason why your film works. No. 2 is Sound. It makes or brakes your picture. Period.
It is amazing to me how little visually talented people recognize that quality of the sound. It is, what creates the illusion in the ambience and focuses the attention of the audience to what’s important: the story. If it sounds like it was recorded in somebody’s a kitchen, it’s very difficult to believe the illusion and get taken on the journey that the filmmaker intended.
There was even a study (PDF) done a couple of years back:
“As an interesting sidelight, we discovered that video with better quality and stereo sound were consistently rated as more likeable, interesting and involving. Viewers also rated programming with better audio as having higher picture quality, but this occurred in only one of the three test programs we ran.”